Objective optical system for endoscopes

ABSTRACT

An objective optical system for endoscopes comprising a plurality of lens components and an aperture stop, and configured so as to permit adjusting a distance to an object to be observed simply by exchanging a lens component disposed in the vicinity of the aperture stop with another lens component having a focal length different from that of the lens component disposed in the vicinity of the aperture stop. This objective optical system for endoscopes can have an optimum depth of field by changing a diameter of the aperture stop along with the exchange of the lens component disposed in the vicinity of the aperture stop.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an objective optical system forendoscopes, and more specifically to an objective optical system forendoscopes which comprises a plurality of lens components including onecomprising an aperture stop and is configured so as to permit adjustinga distance to an object to be observed by disposing one of opticalmembers having focal lengths different from one another selectively inthe vicinity of the aperture stop comprised in the lens component.

2. Description of the Prior Art

In the recent years, there are widely used medical endoscopes whichpermit observing organs in human bodies with slender portions insertedinto human body cavities and elaborately diagnosing abnormal locationsby sampling biological tissues with forceps inserted through forcepschannels as occasion demands. Further, in industrial fields also,industrial endoscopes are widely used for observing and inspectinginteriors of boilors, turbines, engines, chemical plants and so on.

In case of the industrial endoscopes, in particular, a direct viewingtype adaptor is used when an object to be observed is located in frontof a leading end of the slender inserting portion in a longitudinaldirection thereof or a side viewing type adaptor is selected when aninside wall surface or an object to be observed is located in adirection perpendicular to the inserting direction of the insertingportion. For such observation purposes, it is often practised to selectan adaptor which has a field angle optimum for the location of theobject to be observed simultaneously with the adaptor described above.

Since endoscopes are relatively expensive, it is very effective, from aneconomical viewpoint, to provide a leading end adaptor type of endoscopewhich can be equipped with a leading end adaptor having a viewingdirection and a field angle optimum for a location of an object to beobserved. Though the endoscope which is equipped with such a leading endadaptor permits observing an object in an optimum viewing direction andat an optimum field angle, the endoscope requires any focusing means forobserving objects in a variety of observing conditions.

In order to solve the problem described above, the optical system forendoscopes disclosed by Japanese Patent Kokai Publication No. Sho63-291,019 adopts an objective lens system using a means which moves,along an optical axis, certain lens components disposed in the objectivelens system for focusing the optical system on an object to be observedthrough endoscopes. However, such a focusing means disposed in theoptical system to be built in a main body of an endoscope makes itdifficult to configure endoscopes compact and is therefore undesirablefor use in an optical system for endoscopes which are to be configuredcompact.

Further, there are known objective optical systems for endoscopes whichperform focusing by driving objective lens systems with piezoelectricactuators using piezoelectric elements as well as objective opticalsystems for endoscopes which permit remote control of objective lenssystems with manual controllers utilizing force transmitting means suchas wires.

When optical systems for endoscopes are to be focused by movingobjective lens systems, however, the optical systems are apt to requiretedious operations for focusing. When a wire is used as a forcetransmitting means, for example, the wire is built in an insertingportion and is moved by operating a mechanism for bending a distal endor bending the inserting portion, thereby making it difficult to keep anoptical system for endoscopes in an optimum focused condition andinevitably degrading operability of the endoscope which uses the opticalsystem. Further, the optical system which uses the optical systemcomprising the wire requires forcusing operations to be repeated eachtime the endoscope is to be set for observing another object, therebycomplicating operations of the endoscope for observations. When thepiezoelectric actuator is used in place of the wire for moving anobjective lens system, it is difficult to configure a controller for thepiezoelectric actuator and the piezoelectric actuator is alsoundesirable for use in endoscopes which should be configured ascompactly as possible.

Furthermore, there is known a leading end adaptor type endoscope, asexemplified by the one disclosed by Japanese Patent Kokai PublicationNo. Sho 63-298,314, which is configured so as to perform focusing byusing a focusing mechanism disposed in a leading end adaptor to beattached to a front lens component built in an objective lens system.

FIG. 2 shows a sectional view illustrating the leading end of theendoscope and the leading end adaptor. As is seen from this drawing, theleading end of the endoscope has a main body M which comprises anobservation optical system which consists of an objective lens system Oand an image guide fiber bundle IG as well as an illumination lightguide fiber bundle LG disposed in parallel with the observation opticalsystem. Further, disposed in the main body M is a wire passage throughwhich a wire WM having an engaging end E extends to a manual controller.Attached to the other end of the wire WM is a rack R which engages witha pinion PI fixed to a control knob arranged on the manual controller.

On the other hand, a light guide fiber bundle LG, an observation opticalsystem which comprises a negative lens component L₁, another lenscomponent L_(F) attached to a movable frame and a cover glass plate CGare disposed in parallel with each other in the adaptor AD. Attached tothe movable frame is the wire WM having the engaging portion E at oneend thereof. Further, a tapped ring is rotatably fitted over the adaptorAD.

The main body M of the endoscope is coupled with the adaptor in such amanner that optical axes of the illumination light guide fiber bundlesLG disposed therein are aligned with each other and optical axes ofsections of the illumination optical systems disposed therein are alsoaligned with each other, and the adaptor is attached to the main body Mof the endoscope by screwing the tapped ring over thread formed on themain body M of the endoscope. In a condition where the adaptor AD iscoupled with the main body M of the endoscope as described above, thecontrol knob is turned to move the rack R, thereby moving the movableframe back and forth by way of the wire WM.

The endoscope of the type which is configured so as to perform focusingby moving the lens components disposed in the leading end adaptor typeobjective optical system as described above has not only a defect thatit can hardly have high operability and a compact size, but also anotherdefect that it allows aberrations to be aggravated, a field anglethereof to be varied remarkably and hindrance to be caused forobservation when the lens components are moved for a long distance.

Further, the conventional endoscope described above uses an aperturestop having a diameter which is kept fixed for focusing. Therefore, thisendoscope provides brightness insufficient for observation of an objectlocated at a long distance when the diameter of the aperture stop issmall, for example, to obtain a large depth of field for observing anobject located at a short distance. When the diameter of the aperturestop is large for obtaining brightness sufficient for observing anobject located at a long distance, in contrast, the endoscope has adepth of field too small for observing an object located at a longdistance and is therefore insufficient for practical use. On the otherhand, an endoscope which is equipped with an automatic iris requires alarge mechanism for controlling an aperture stop and is thereforeundesirable as a practical endoscope.

SUMMARY OF THE INVENTION

A primary object of the present invention is to provide an objectiveoptical system for endoscopes which is compact, features highoperability and has a means for adjusting a distance to an object to beobserved.

The objective optical system for endoscopes according to the presentinvention comprises a plurality of lens components and an aperture stop,and is characterized in that it permits adjusting the distance to theobject to be observed by exchanging one of the lens components which isdisposed in the vicinity of the aperture stop with another lenscomponent having a focal length different from that oft he former lenscomponent.

FIG. 3 shows a sectional view illustrating a fundamental composition ofa leading end adaptor type objective optical system for endoscopes whichis preferred as a typical example of the objective optical system forendoscopes according to the present invention. As is seen from thisdrawing, the objective optical system for endoscopes according to thepresent invention consists of:an optical system which is to be disposedin a main body of an endoscope, and consists of an objective lens system6 and an image transmission system 8 for transmitting an image 7 formedby the objective lens system 6; and an objective lens system 2 which isto be disposed in an adaptor, and consists of a plurality of lenscomponents 3 and 5 disposed on an object side end surface of the opticalsystem 1 as well as an aperture stop 4. The objective lens system 2disposed in the adaptor is exchangeable with another adaptor sideobjective lens system 2' or 2" which comprises a lens component 5' or 5"different from the lens component 5 so that the endoscope can have adesired object distance.

Out of the adaptor side objective lens systems 2, 2' and 2", theobjective lens system 2 uses a plane parallel plate 5 as the lenscomponent disposed in the vicinity of the aperture stop 4 so that theobject distance of the objective optical system which is determineddependently on a refractive power distribution between the lenscomponents 3 is not influenced due to the lens component disposed in thevicinity of the aperture stop 4. In the adaptor side objective lenssystem 2', the lens component disposed in the vicinity of the aperturestop is a positive lens component 5' having a convex surface on the sideof the aperture stop so as to obtain an object distance L_(n) which isshorter than an object distance L determined dependently on therefractive power distribution in the lens system 3. Further, in theadaptor side objective lens system 2", the lens component disposed inthe aperture stop is a negative lens component 5" which has a concavesurface on the side of the aperture stop for obtaining an objectdistance L_(f) which is longer than the object distance L determineddependently on the refractive power distribution in the lens components3.

Furthermore, the adaptor side objective lens systems 2, 2' and 2" havefield angles each nearly equal to a field angle of 2ω which isdetermined dependently on the refractive power distribution in thecommon lens components 3 and almost free from influence due to the lenscomponents 5, 5' and 5" disposed in the vicinity of the aperture stop.In other words, the objective optical system for endoscopes according tothe present invention has a field angle which is determined by aprincipal ray and scarecely varied by refraction due to the lenscomponent 5, 5' or 5" since the principal ray has a height which can beregarded as zero on this lens component. Therefore, the field angle ofthe objective optical system for endoscopes according to the presentinvention can be kept constant even when the object distance is adjustedby varying a refractive power of the lens component disposed in thevicinity of the aperture stop.

When the adaptor side objective lens system 2, 2' or 2" is connected tothe objective lens system 6 which is disposed in the main body M of theendoscope, a spacing between the objective lens systems is oftendeviated from a value predetermined therefor due to manufacturing errorswithin allowances specified for parts. For reducing an influence on theobject distance L, L_(n) or L_(f) due to such a deviation of thespacing, it is desirable to configure the objective lens system 6 whichis to be disposed in the main body M of the endoscope so as to form animage 7 at a location of a rear focal point of the objective lens system6. In other words, it is desirable that a light bundle emerging from theadaptor side objective lens system 2, 2' or 2" is composed of rays whichare parallel with one another.

As is understood from the foregoing description, the objective opticalsystem for endoscopes according to the present invention consists of aplurality of lens components 3, 5, 6 and an aperture stop 4 asillustrated in FIG. 3. Speaking more concretely, the objective opticalsystem for endoscopes according to the present invention consists of:theadaptor side objective lens system which is composed of the lenscomponents 3 and 5, out of the plurality of lens components, and theaperture stop 4; and the objective lens system 6 to be disposed in themain body M of the endoscope which is composed of at least one lenscomponent (two lens components in the objective lens system shown inFIG. 3). The object distance L_(f) of the objective optical system forendoscopes according to the present invention is changed to a differentobject distance L_(n) or L_(f) by exchanging the lens component 5 whichis disposed in the vicinity of the aperture stop 4 with the lenscomponent 5' or 5" having a focal length different from that of the lenscomponent 5.

For obtaining a light bundle composed of rays which are nearly parallelwith one another, it is desirable to select, within the range definedbelow, a distance Δf_(B6) as measured from a paraxial image point 7 to arear focal point of the objective lens system 6 which is disposed in themain body M of the endoscope (a rear optical unit which is composed ofthe lens components disposed on the emergence side of the exchangeablelens component 5 disposed in the vicinity of the aperture stop 4):

    50×f.sub.6.sup.2 ÷1000≧|Δf.sub.B6 |

This formula can be transformed as follows:

    |Δf.sub.B6 /f.sub.6.sup.2 ≦0.05

wherein the reference symbol f₆ represents a focal length of theobjective lens system 6 to be disposed in the main body M of theendoscope (the rear optical unit which is composed of the lenscomponents disposed on the emergence side of the exchangeable lenscomponent 5 disposed in the vicinity of the aperture stop 4).

If Δf_(B6) is large enough to exceed the range defined by theabove-mentioned condition, a light bundle which is to be incident on theobjective lens system 6 disposed in the main body M of the endoscopewill undesirably be divergent or convergent.

When a convergent light bundle is to be incident on the objective lens6, the spacing between the adaptor side objective lens system 2, 2' or2" and the objective lens system 6 disposed in the main body M of theendoscope will be narrower than the predetermined value and theobjective optical system for endoscopes will be focused on the objectdistance L_(f) which is longer than the predetermined object distance L.When a divergent light bundle is to be incident on the objective lenssystem 6, in contrast, the spacing will be larger than the predeterminedvalue and the objective optical system for endoscopes will undesirablybe focused on an object distance which is shorter than the predeterminedobject distance L.

When a light bundle which is composed of rays nearly parallel with oneanother is to be incident on the objective lens system 6, the objectdistance L shown in FIG. 3 will be nearly coincident with a distance asmeasured from a principal point to a front focal point of the adaptorside objective lens system 2 (i.e., the lens components 3). When thelens component 5 which is disposed in the vicinity of the aperture stop4 is exchanged with the lens component 5' or 5", the objective opticalsystem is focused on an object distance described below:

When a focal length of the lens components 3 is represented by f₃, afront focal point of the adaptor side objective lens system 2' or 2" isdesignated by f_(F2), a focal length of the lens component 5' or 5" isdenoted by f₅ and a distance as measured from a principal point of thelens components 3 to a principal point of the lens component 5' or 5" isrepresented by d, the adaptor side objective lens system 2' or 2" has afocal length f₂ which is expressed by the following formula (1):

    f.sub.2 =f.sub.3 ·f.sub.5 /(f.sub.5 -f.sub.3 -d)  (1)

Further, the front focal point f_(F3) on an object distance is expressedby the following formula (2):

    f.sub.F3 =f.sub.2 {(f.sub.5 -d)/f.sub.5 }                  (2)

However, since the objective optical system for endoscopes actually hasan object distance which is as measured from a first surface thereof toan object to be observed, the object distance can be expressed by thefollowing formula (2'):

    f.sub.F3 =f.sub.2 {(f.sub.5 -d)/f.sub.5 }-d'               (2')

wherein the reference symbol d' represents a distance as measured from afront principal point H of the objective optical system 2' or 2" to thefirst surface of the objective optical system for endoscopes.

In this case, the object distance is changed by varying the focal lengthf₅ of the lens component which is disposed in the vicinity of theaperture stop arranged in the leading end adaptor. That is to say, thefollowing formula (3) is obtained from the above-mentioned formula (2'):

    f.sub.5 =d·f.sub.2 /(f.sub.2 -f.sub.F3 -d')       (3)

In this case, the field angle 2ω is scarecely varied. That is to say,the focal length f₂ of the objective lens system 2, 2' or 5" whichcomprises the lens component 5, 5' or 5" as a whole is scarecely varied.When the lens component 5' or 5" is disposed with a certain space fromthe aperture stop, however, the field angle 2ω is largely varied, or thefocal length f₂ of the adaptor side objective lens system is varied. Asa result, it is desirable that the lens component 5' or 5" is disposedin the vicinity of the aperture stop so that ω is allowed to be variedwithin a range of 15%.

Since relationship between an image height and a field angle of anordinary objective optical system for endoscopes (a telecentric opticalsystem) is expressed as h=f·sin θ, it is desirable that the objectiveoptical system satisfies the following condition:

    |{sin.sup.-1 (h/f)-sin.sup.-1 (h/f')}/sin.sup.-1 (h/f)|≦0.15

wherein the reference symbol h represents a maximum image height in theobjective optical system, the reference symbol f designates a totalfocal length of the lens components 3 and 5 of the adaptor lens unit andthe objective lens system 6 which is disposed in the main body of theendoscope (a focal length of the objective optical system for endoscopesas a whole), and the reference symbol f' denotes a focal length of theobjective optical system for endoscopes as a whole when the lenscomponent 5 of the adaptor side objective lens system is exchanged withthe lens component 5' or 5".

When the objective optical system for endoscopes is to be used forobserving an object located at a short distance which is to beilluminated sufficiently brightly with a light bundle emerging from thelight guide fiber bundle built in the inserting portion, it is desirableto enlarge an F number and a depth of field of the objective opticalsystem by reducing the diameter of the aperture stop. When the objectiveoptical system for endoscopes is to be used for observing an objectlocated at a long distance which is to be illuminated with insufficientbrightness, it is desirable to reduce the F number of the objectiveoptical system by enlarging the diameter of the aperture stop.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view illustrating a composition of aconventional objective optical system for endoscopes;

FIG. 2 shows a sectional view illustrating a composition of aconventional leading end adaptor type objective optical system forendoscopes;

FIG. 3 shows a sectional view illustrating a fundamental composition ofthe objective optical system for endoscopes according to the presentinvention;

FIG. 4 shows a diagram illustrating relationship between compositions ofthe objective optical system for endoscopes according to the presentinvention and objective distances thereof;

FIG. 5 and FIG. 6 show sectional views of a first embodiment of thepresent invention;

FIG. 7 and FIG. 8 show sectional views illustrating compositions of afirst embodiment of the objective optical system for endoscopesaccording to the present invention;

FIG. 9 and FIG. 10 show sectional views illustrating structures of asecond embodiment of the present invention;

FIG. 11 and FIG. 12 show sectional views illustrating compositions of anobjective optical system for endoscopes which is to be used in thesecond embodiment of the present invention;

FIG. 13 and FIG. 14 show sectional views illustrating compositions of anobjective optical system for endoscopes which is preferred as a thirdembodiment of the present invention;

FIG. 15 and FIG. 16 show sectional views illustrating compositions of anobjective optical system for endoscopes which is preferred as a fourthembodiment of the present invention;

FIG. 17 and FIG. 18 show sectional views illustrating compositions of anobjective optical system for endoscopes which is preferred as a fifthembodiment of the present invention;

FIG. 19 and FIG. 20 show sectional views illustrating compositions of anobjective optical system for endoscopes which is preferred as a sixthembodiment of the present invention;

FIG. 21 and FIG. 22 show sectional view illustrating compositions of anobjective optical system for endoscopes which is preferred as a seventhembodiment of the present invention;

FIG. 23 and FIG. 24 show graphs illustrating aberration characteristicsof the first embodiment of the objective optical system for endoscopesaccording to the present invention when the objective optical system isset for observing an object located at a long distance and at a shortdistance respectively;

FIG. 25 and FIG. 26 show graphs illustrating aberration characteristicsof the second embodiment of the objective optical system for endoscopesaccording to the present invention when it is set for observing anobject located at a long distance and at a short distance respectively;

FIG. 27 and FIG. 28 show graphs illustrating aberration characteristicsof the third embodiment of the objective optical system for endoscopesaccording to the present invention when it is set for observing anobject located at a long distance and at a short distance respectively;

FIG. 29 and FIG. 30 show graphs illustrating aberration characteristicsof the fourth embodiment of the objective optical system for endoscopesaccording to the present invention when it is set for observing anobject located at a long distance and at a short distance respectively;

FIG. 31 and FIG. 32 show curves visualizing aberration characteristicsof the fifth embodiment of the objective optical system for endoscopesaccording to the present invention when it is set for observing anobject located at a long distance and at a short distance respectively;

FIG. 33 and FIG. 34 show curves visualizing aberration characteristicsof the sixth embodiment of the objective optical system for endoscopesaccording to the present invention when it is set for observing anobject located at a long distance and at a short distance respectively;

FIG. 35 and FIG. 36 shows curves visualizing aberration characteristicsof the seventh embodiment of the objective optical system for endoscopesaccording to the present invention when it is set for observing anobject located at a long distance and at a short distance respectively;

FIG. 37 shows a sectional view illustrating a composition of an eighthembodiment of the objective optical system for endoscopes according tothe present invention;

FIG. 38 show graphs illustrating aberration characteristics of theeighth embodiment of the objective optical system for endoscopesaccording to the present invention; and

FIG. 39 through FIG. 44 show graphs illustrating spectroscopictransmittance characteristics of radiation-resistant glass materials.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the objective optical system for endoscopes according to thepresent invention will be described more detailedly below with referenceto the preferred embodiments thereof illustrated in the accompanyingdrawings.

FIG. 5 shows a sectional view illustrating the composition of the firstembodiment of the objective optical system for endoscopes according tothe present invention, wherein a direct viewing type leading end adaptorwhich has a field angle of 100° is attached to a main body of anendoscope.

In this drawing, the reference numeral 10 represents the main body ofthe endoscope having a leading end (a master lens unit) 20 to which anadaptor unit 30 is attached. Disposed in a lens barrel which issustained in the main body 10 are a cover glass plate C₁, an infraredlight cutoff filter F₁ and a lens element L₄ which are arranged withflare stops FS₁ and FS₂ interposed therebetween, whereas a spacing tubeserving also as a flare stop FS₄ and a lens component L₅ which consistsof lens elements L₅ ' and L₅ " are fixed on the image side. Thesemembers are inserted into an optical insertion hole 14 formed in amember 12 which composes an object side leading end of the lens barrel11, and cemented or fixed therein.

Furthermore, fitted over an outside wall of the lens barrel 11 is animage pickup unit 16 in which a flare stop FS₃, a field lens FL, a lowpass filter F₂, a cover glass plate C₂ and an image pickup element 15are cemented or fixed. This image pickup unit 16 is fixed after it isshifted along the optical axis and a focal point of the objective lenssystem 6 which is disposed in the main body of the endoscope (the coverglass plate C₁, the infrared light cutoff filter F₁, the lens componentL₄, the lens component L₅ consisting of the lens elements L₅ ' and L₅ ",the field lens FL, the low pass filter F₂, and the cover glass plate C₂)is adjusted.

Furthermore, formed in the leading end composing member 12 is a hole 17into which a light guide fiber bundle LG having a cover glass plate C₃cemented to a tip thereof is to be inserted. The light guide fiberbundle LG has the other end which is to be connected to a light sourceby way of a universal cord (not shown) passing throughout the main bodyof the endoscope.

On the other hand, the leading end adaptor unit 30 is attached to afixing member 21 of the leading end master lens unit 20 of the main body10 of the endoscope by screwing male threads 24 of a fixing member 23for the main body into tapping 22 of an adaptor fixing member 21.Further, a lens component L₁ which is used for composing the objectivelens system 2 is cemented or fixed on the side of the leading end in anobservation hole 31 formed in the leading end adaptor unit 30 with aflare stop FS made of a thin metal plate interposed between a surface 33of an adaptor composing member 32 and the lens component L₁. On the sideof the main body of the endoscope in the observation hole 31 formed inthe adaptor unit 30, a lens component L₂, a spacing tube 34 serving alsoas an aperture stop AS and a cover glass plate C₅ (L₃) are consecutivelyinserted and cemented or fixed.

Moreover, on the leading end, a light guide rod 41 on which anillumination lens 40 is mounted is cemented or fixed in an illuminationsystem insertion hole 43 formed in the adaptor composing member 32.

FIG. 6 shows a sectional view illustrating a direct viewing type leadingend adaptor 50 for observing an object located at a short distance.Disposed in this adaptor unit 50 are a spacing tube 53 which has anarrowed portion for composing an aperture stop AS' having a smalldiameter, unlike the spacing tube 34 of the direct viewing type leadingend adaptor unit 30 for observing the object located as the longdistance shown in FIG. 5, lens components L₁ and L₂, and a lenscomponent L₃ ' (a focal point adjusting lens component) having a convexsurface to be brought into contact with the aperture stop AS' of thespacing tube 53 which is adopted in place of the cover glass plate C₅(L₃) used for the direct viewing type adaptor unit for observing theobject located at the long distance. This lens component L₃ ' is adoptedfor making the adaptor unit 50 suited for observing an object located ata distance which is shorter than that of the object to be observed byusing the direct viewing type leading end adaptor for observing theobject located at the long distance. In addition, the focal pointadjusting lens component L₃ ' shown in FIG. 6 is chamfered on the sideof the spacing tube 53 so that surfaces having curvature can bediscriminated.

FIG. 7 and FIG. 8 show sectional views illustrating objective lenssystems which are to be used in the first embodiment of the presentinvention. FIG. 7 shows a direct viewing type objective lens system forobserving an object located at a long distance, whereas FIG. 8 shows adirect viewing type objective optical system for observing an objectlocated at a short distance; these objective lens systems having thenumerical data listed below:

Embodiment 1

for observing object at long distance

f=1.000, image height=0.8088, f_(B) =0.021,

2ω=100.27°, object distance=-42.7960

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.2853                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8845                                                                d.sub.2 = 0.4280                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.5492                                                            r.sub.4 = ∞                                                               d.sub.4 = 0.7846                                                                           n.sub.2 = 1.63930                                                                          ν.sub.2 = 44.88                                r.sub.5 = -1.5449                                                               d.sub.5 = 0.4636                                                            r.sub.6 = ∞ (stop)                                                        d.sub.6 = 0.3210                                                                           n.sub.3 = 1.88300                                                                          ν.sub.3 = 40.78                                r.sub.7 = ∞                                                               d.sub.7 = 0.1070                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.2853                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = ∞                                                               d.sub.9 = 0.0214                                                            r.sub.10 = ∞                                                              d.sub.10 = 1.4265                                                                          n.sub.5 = 1.52000                                                                          ν.sub.5 = 74.00                                r.sub.11 = ∞                                                              d.sub.11 = 0.0214                                                           r.sub.12 = ∞                                                              d.sub.12 = 0.4280                                                                          n.sub.6 = 1.62280                                                                          ν.sub.6 = 57.06                                r.sub.13 = -2.5678                                                              d.sub.13 = 0.0713                                                           r.sub.14 = 2.1897                                                               d.sub.14 = 0.9272                                                                          n.sub.7 = 1.65844                                                                          ν.sub.7 = 50.86                                r.sub.15 = -1.3966                                                              d.sub.15 = 0.2710                                                                          n.sub.8 = 1.75520                                                                          ν.sub.8 = 27.51                                r.sub.16 = 2.1897                                                               d.sub.16 = 0.5421                                                           r.sub.17 = ∞                                                              d.sub.17 = 0.0000                                                           r.sub.18 = 2.7832                                                               d.sub.18 = 0.4993                                                                          n.sub.9 = 1.77250                                                                          ν.sub.9 = 49.66                                r.sub.19 = ∞                                                              d.sub.19 = 0.9344                                                                          n.sub.10 = 1.54814                                                                         ν.sub.10 = 45.78                               r.sub.20 = ∞                                                              d.sub.20 = 0.2853                                                                          n.sub.11 = 1.52287                                                                         ν.sub.11 = 59.89                               r.sub.21 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0031524674            ______________________________________                                    

for observing object at short distance

f=1.000, image height=0.8141, f_(B) =0.011,

2ω=100.34°, object distance=-10.3374

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.2872                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.8902                                                                d.sub.2 = 0.4307                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.5528                                                            r.sub.4 = ∞                                                               d.sub.4 = 0.7897                                                                           n.sub.2 = 1.63930                                                                          ν.sub.2 = 44.88                                r.sub.5 = -1.5549                                                               d.sub.5 = 0.4666                                                            r.sub.6 = 68.4235 (stop)                                                        d.sub.6 = 0.3230                                                                           n.sub.3 = 1.88300                                                                          ν.sub.3 = 40.78                                r.sub.7 = ∞                                                               d.sub.7 = 0.1077                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.2872                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = ∞                                                               d.sub.9 = 0.0215                                                            r.sub.10 = ∞                                                              d.sub.10 = 1.4358                                                                          n.sub.5 = 1.52000                                                                          ν.sub.5 = 74.00                                r.sub.11 = ∞                                                              d.sub.11 = 0.0215                                                           r.sub.12 = ∞                                                              d.sub.12 = 0.4307                                                                          n.sub.6 = 1.62280                                                                          ν.sub.6 = 57.06                                r.sub.13 = -2.5844                                                              d.sub.13 = 0.0718                                                           r.sub.14 = 2.2039                                                               d.sub.14 = 0.9332                                                                          n.sub.7 = 1.65844                                                                          ν.sub.7 = 50.86                                r.sub.15 = -1.4056                                                              d.sub.15 = 0.2728                                                                          n.sub.8 = 1.75520                                                                          ν.sub.8 = 27.51                                r.sub.16 = 2.2039                                                               d.sub.16 = 0.5456                                                           r.sub.17 = ∞                                                              d.sub.17 = 0.0000                                                           r.sub.18 = 2.8011                                                               d.sub.18 = 0.5025                                                                          n.sub.9 = 1.77250                                                                          ν.sub.9 = 49.66                                r.sub.19 = ∞                                                              d.sub.19 = 0.9404                                                                          n.sub.10 = 1.54814                                                                         ν.sub.10 = 45.78                               r.sub.20 = ∞                                                              d.sub.20 = 0.2872                                                                          n.sub.11 = 1.52287                                                                         ν.sub.11 = 59.89                               r.sub.21 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0047572483            |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0.0006981151                                                              ______________________________________                                    

wherein the reference symbols r₁, r₂, . . . represent radii of curvatureon surfaces of the respective lens elements, the reference symbols d₁,d₂, . . . designate airspaces reserved between the surfaces of therespective lens elements, the reference symbols n₁, n₂, . . . denoterefractive indices of the respective optical elements, and the referencesymbols ν₁, ν₂, . . . represent Abbe's numbers of the respective opticalelements.

In the first embodiment of the objective optical system for endoscopesaccording to the present invention described above, the focal pointadjusting lens component which is to be used for observing the objectlocated at the long distance has a planar surface r₆, whereas the focalpoint adjusting lens component which is to be adopted for observing theobject located at short distance has a convex surface r₆.

FIG. 9 and FIG. 10 show sectional views illustrating the secondembodiment of the present invention. Out of these drawings, FIG. 9 showsa side viewing type leading end adaptor which is to be used forobserving an object located at a long distance and has a field angle of100°, whereas FIG. 10 shows a side viewing type leading end adaptorwhich is to be employed for observing an object located at a shortdistance.

A leading end adaptor unit 60 shown in FIG. 9 comprises: a lenscomponent L₁, which is used for composing an objective lens system 2 tobe disposed on an adaptor unit, cemented or fixed in an observation hole61 formed on one side of a longitudinal centerline thereof with a flarestop 63 made of a thin metal plate interposed between a surface 63 of anadaptor composing member 62 and the lens component L₁ ; a viewingdirection changing prism P which is supported, under the observationhole 61, by a surface 64 of the adaptor composing member 62, a side wall(not shown) of an observation window and a tip 66 of a lens barrel 65,and cemented or fixed to these members; and a lens component L₂, aspacing the 67 serving also as a flare stop, optical path adjustingglass member 68, an aperture stop AS made of a thin metal plate and acover glass plate C which are inserted into the lens barrel 65 in anorder from the side of the tip thereof and cemented or fixed to the lensbarrel 65. The optical path adjusting glass member 68 is used forreserving a space for an adaptor side fixing member 70 over the lensbarrel 65.

Further, an illumination lens 71 is cemented or fixed in an illuminationsystem insertion hole formed in the adaptor composing member 62 and alight guide fiber bundle LG extends from a location in the vicinity of aconcave surface of the illumination lens 71 to a location correspondingto an illumination window formed in the leading end of the main body ofthe endoscope and cemented or fixed to the light guide fiber bundleinsertion hole formed in the lens barrel 65.

A side viewing type leading end adaptor unit 80 for observing an objectlocated at a short distance shown in FIG. 10 uses, in place of theaperture stop adopted in the side viewing type leading end adaptor unit60, an aperture stop which has a small diameter for observing an objectlocated at a short distance so that the objective optical system forendoscopes has a large depth of field. Further, this leading end adaptorunit 80 adopts a focal point adjusting lens component L₃ ', in place ofthe cover glass plate C of the side viewing type leading end adaptor 60for observing the object located at the long distance, which adjusts thefocal point so that the leading end adaptor unit 80 is suited forobserving an object located at a distance shorter than the objectdistance of the side viewing type leading end adaptor unit 60 forobserving the object located at the long distance. In the secondembodiment also, the focal point adjusting lens component L₃ ' ischamfered on the side of the main body of the endoscope for facilitatingdiscrimination of surfaces having curvature.

The objective optical system for endoscopes preferred as the secondembodiment has the compositions illustrated in FIG. 11 and FIG. 12, andnumerical data which are listed below:

Embodiment 2

for observing object at long distance

f=1.000, image height=0.8265, f_(B) =0.012,

2ω=99.368°, object distance=-8.7464

    ______________________________________                                        r.sub.1 = 13.8491                                                               d.sub.1 = 0.2551                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.9446                                                                d.sub.2 = 0.3644                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.1458                                                            r.sub.4 = ∞                                                               d.sub.4 = 1.6764                                                                           n.sub.2 = 1.88300                                                                          ν.sub.2 = 40.78                                r.sub.5 = ∞                                                               d.sub.5 = 0.0802                                                            r.sub.6 = ∞                                                               d.sub.6 = 0.4665                                                                           n.sub.3 = 1.60342                                                                          ν.sub.3 = 38.01                                r.sub.7 = -1.6603                                                               d.sub.7 = 0.0729                                                            r.sub.8 = ∞                                                               d.sub.8 = 1.2391                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = ∞                                                               d.sub.9 = 0.0219                                                            r.sub.10 = ∞ (stop)                                                       d.sub.10 = 0.3280                                                                          n.sub.5 = 1.88300                                                                          ν.sub.5 = 40.78                                r.sub.11 = ∞                                                              d.sub.11 = 0.1093                                                           r.sub.12 = ∞                                                              d.sub.12 = 0.2915                                                                          n.sub.6 = 1.88300                                                                          ν.sub.6 = 40.78                                r.sub.13 = ∞                                                              d.sub.13 = 0.0219                                                           r.sub.14 = ∞                                                              d.sub.14 = 1.4577                                                                          n.sub.7 = 1.52000                                                                          ν.sub.7 = 74.00                                r.sub.15 = ∞                                                              d.sub.15 = 0.0219                                                           r.sub.16 = ∞                                                              d.sub.16 = 0.4373                                                                          n.sub.8 = 1.62280                                                                          ν.sub.8 = 57.06                                r.sub.17 = -2.6239                                                              d.sub.17 = 0.0729                                                           r.sub.18 = 2.2376                                                               d.sub.18 = 0.9475                                                                          n.sub.9 = 1.65844                                                                          ν.sub.9 = 50.86                                r.sub.19 = -1.4271                                                              d.sub.19 = 0.2770                                                                          n.sub.10 = 1.75520                                                                         ν.sub.10 = 27.51                               r.sub.20 = 2.2376                                                               d.sub.20 = 0.5539                                                           r.sub.21 = ∞                                                              d.sub.21 = 0.0000                                                           r.sub.22 = 2.8440                                                               d.sub.22 = 0.5102                                                                          n.sub.11 = 1.77250                                                                         ν.sub.11 = 49.66                               r.sub.23 = ∞                                                              d.sub.23 = 0.9548                                                                          n.sub.12 = 1.54814                                                                         ν.sub.12 = 45.78                               r.sub.24 = ∞                                                              d.sub.24 = 0.2915                                                                          n.sub.13 = 1.52287                                                                         ν.sub.13 = 59.89                               r.sub.25 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0046141247            ______________________________________                                    

for observing object at short distance

f=1.000, image height=0.8314, f_(B) =0.013,

2ω=99.568°, object distance=-5.1320

    ______________________________________                                        r.sub.1 = 13.9304                                                               d.sub.1 = 0.2566                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 0.9501                                                                d.sub.2 = 0.3666                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.1466                                                            r.sub.4 = ∞                                                               d.sub.4 = 1.6862                                                                           n.sub.2 = 1.88300                                                                          ν.sub.2 = 40.78                                r.sub.5 = ∞                                                               d.sub.5 = 0.0806                                                            r.sub.6 = ∞                                                               d.sub.6 = 0.4692                                                                           n.sub.3 = 1.60342                                                                          ν.sub.3 = 38.01                                r.sub.7 = -1.6701                                                               d.sub.7 = 0.0733                                                            r.sub.8 = ∞                                                               d.sub.8 = 1.2463                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = ∞                                                               d.sub.9 = 0.0220                                                            r.sub.10 = ∞ (stop)                                                       d.sub.10 = 0.3299                                                                          n.sub.5 = 1.88300                                                                          ν.sub.5 = 40.78                                r.sub.11 = -90.7705                                                             d.sub.11 = 0.1100                                                           r.sub.12 = ∞                                                              d.sub.12 = 0.2933                                                                          n.sub.6 = 1.88300                                                                          ν.sub.6 = 40.78                                r.sub.13 = ∞                                                              d.sub.13 = 0.0220                                                           r.sub.14 = ∞                                                              d.sub.14 = 1.4663                                                                          n.sub.7 = 1.52000                                                                          ν.sub.7 = 74.00                                r.sub.15 = ∞                                                              d.sub.15 = 0.0220                                                           r.sub.16 = ∞                                                              d.sub.16 = 0.4399                                                                          n.sub.8 = 1.62280                                                                          ν.sub.8 = 57.06                                r.sub.17 = -2.6393                                                              d.sub.17 = 0.0733                                                           r.sub.18 = 2.2507                                                               d.sub.18 = 0.9531                                                                          n.sub.9 = 1.65844                                                                          ν.sub.9 = 50.86                                r.sub.19 = -1.4355                                                              d.sub.19 = 0.2786                                                                          n.sub.10 = 1.75520                                                                         ν.sub.10 = 27.51                               r.sub.20 = 2.2507                                                               d.sub.20 = 0.5572                                                           r.sub.21 = ∞                                                              d.sub.21 = 0.0000                                                           r.sub.22 = 2.8607                                                               d.sub.22 = 0.5132                                                                          n.sub.11 = 1.77250                                                                         ν.sub.11 = 49.66                               r.sub.23 = ∞                                                              d.sub.23 = 0.9604                                                                          n.sub.12 = 1.54814                                                                         ν.sub.12 = 45.78                               r.sub.24 = ∞                                                              d.sub.24 = 0.2933                                                                          n.sub.13 = 1.52287                                                                         ν.sub.13 = 59.89                               r.sub.25 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0044021807            |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0.0020127204                                                              ______________________________________                                    

In the second embodiment, a surface r₁₁ for observing the object locatedat the long distance is planar, whereas a surface r₁₁ for observing theobject located at the short distance is convex.

FIG. 13 and FIG. 14 show sectional views illustrating compositions of adirect viewing type objective optical system for endoscopes which ispreferred as the third embodiment of the present invention. FIG. 13shows a direct viewing type objective lens system for observing anobject located at a long distance, whereas FIG. 14 shows a directviewing type objective lens system for observing an object located at ashort distance. These objective lens systems have numerical data whichare listed below:

Embodiment 3

for observing object at long distance

f=1.000, image height=0.5108, f_(B) =-0.002,

2ω=58.996°, object distance=-31.5315

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.1802                                                                           n.sub.1 = 1.51633                                                                          ν.sub.1 = 64.15                                r.sub.2 = 0.7423                                                                d.sub.2 = 0.1802                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.5135                                                            r.sub.4 = 2.5468                                                                d.sub.4 = 0.2973                                                                           n.sub.2 = 1.61700                                                                          ν.sub.2 = 62.79                                r.sub.5 = -2.5468                                                               d.sub.5 = 0.1757                                                            r.sub.6 = ∞ (stop)                                                        d.sub.6 = 0.2027                                                                           n.sub.3 = 1.88300                                                                          ν.sub.3 = 40.78                                r.sub.7 = ∞                                                               d.sub.7 = 0.0676                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.1802                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = ∞                                                               d.sub.9 = 0.0135                                                            r.sub.10 = ∞                                                              d.sub.10 = 0.9009                                                                          n.sub.5 = 1.52000                                                                          ν.sub.5 = 74.00                                r.sub.11 = ∞                                                              d.sub.11 = 0.0135                                                           r.sub.12 = ∞                                                              d.sub.12 = 0.2703                                                                          n.sub.6 = 1.62280                                                                          ν.sub.6 = 57.06                                r.sub.13 = -1.6216                                                              d.sub.13 = 0.0450                                                           r.sub.14 = 1.3829                                                               d.sub.14 = 0.5856                                                                          n.sub.7 = 1.65844                                                                          ν.sub.7 = 50.86                                r.sub.15 = -0.8820                                                              d.sub.15 = 0.1712                                                                          n.sub.8 = 1.75520                                                                          ν.sub.8 = 27.51                                r.sub.16 = 1.3829                                                               d.sub.16 = 0.3423                                                           r.sub.17 = ∞                                                              d.sub.17 = 0.0000                                                           r.sub.18 = 1.7577                                                               d.sub.18 = 0.3153                                                                          n.sub.9 = 1.77250                                                                          ν.sub.9 = 49.66                                r.sub.19 = ∞                                                              d.sub.19 = 0.5901                                                                          n.sub.10 = 1.54814                                                                         ν.sub.10 = 45.78                               r.sub.20 = ∞                                                              d.sub.20 = 0.1802                                                                          n.sub.11 = 1.52287                                                                         ν.sub.11 = 59.89                               r.sub.21 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0095857258            ______________________________________                                    

for observing object at short distance

f=1.000, image height=0.5157, f_(B) =0.000,

2ω=58.984°, object distance=-8.6403

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.1819                                                                           n.sub.1 = 1.51633                                                                          ν.sub.1 = 64.15                                r.sub.2 = 0.7494                                                                d.sub.2 = 0.1819                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.5184                                                            r.sub.4 = 2,5712                                                                d.sub.4 = 0.3001                                                                           n.sub.2 = 1.61700                                                                          ν.sub.2 = 62.79                                r.sub.5 = -2.5712                                                               d.sub.5 = 0.1774                                                            r.sub.6 = 28.3893 (stop)                                                        d.sub.6 = 0.2046                                                                           n.sub.3 = 1.88300                                                                          ν.sub.3 = 40.78                                r.sub.7 = ∞                                                               d.sub.7 = 0.0682                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.1819                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = ∞                                                               d.sub.9 = 0.0136                                                            r.sub.10 = ∞                                                              d.sub.10 = 0.9095                                                                          n.sub.5 = 1.52000                                                                          ν.sub.5 = 74.00                                r.sub.11 = ∞                                                              d.sub.11 = 0.0136                                                           r.sub.12 = ∞                                                              d.sub.12 = 0.2729                                                                          n.sub.6 = 1.62280                                                                          ν.sub.6 = 57.06                                r.sub.13 = -1.6371                                                              d.sub.13 = 0.0455                                                           r.sub.14 = 1.3961                                                               d.sub.14 = 0.5912                                                                          n.sub.7 = 1.65844                                                                          ν.sub.7 = 50.86                                r.sub.15 = -0.8904                                                              d.sub.15 = 0.1728                                                                          n.sub.8 = 1.75520                                                                          ν.sub.8 = 27.51                                r.sub.16 = 1.3961                                                               d.sub.16 = 0.3456                                                           r.sub.17 = ∞                                                              d.sub.17 = 0.0000                                                           r.sub.18 = 1.7744                                                               d.sub.18 = 0.3183                                                                          n.sub.9 = 1.77250                                                                          ν.sub.9 = 49.66                                r.sub.19 = ∞                                                              d.sub.19 = 0.5957                                                                          n.sub.10 = 1.54814                                                                         ν.sub.10 = 45.78                               r.sub.20 = ∞                                                              d.sub.20 = 0.1819                                                                          n.sub.11 = 1.52287                                                                         ν.sub.11 = 59.89                               r.sub.21 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0102203675            |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0.0002034036                                                              ______________________________________                                    

In the third embodiment of the present invention, a surface r₆ which isto be used for observing the object located at the long distance isplanar and a surface r₆ which is to be employed for observing the objectlocated at the short distance is convex.

FIG. 15 and FIG. 16 show sectional views illustrating compositions of aleading end adaptor type objective optical system for endoscope having afield angle of 60° which is preferred as the fourth embodiment of thepresent invention, in which an optical fiber bundle is used as an imagetransmission system. FIG. 15 shows a sectional view illustrating theobjective optical system for endoscopes in a condition where it isequipped with a direct viewing type adaptor for observing an objectlocated at a long distance, whereas FIG. 16 shows a sectional viewillustrating the objective optical system for endoscopes in anothercondition where it is equipped with a direct viewing type leading endadaptor for observing an object located at a short distance.

The fourth embodiment consists of:a leading end adaptor which iscomposed of a negative lens component L₁, a positive lens component L₂,an aperture stop AS and a focal point adjusting lens component L₃ ; apositive lens component L₄ ; a cemented lens component L₅ which iscomposed of a positive lens element L₅ ' and a negative lens element L₅"; a cover glass plate C; an image guide IG made of an optical fiberbundle. In the objective optical system for endoscopes shown in FIG. 16,the adaptor which uses the focal point adjusting lens component L₃ isexchanged with another adaptor which uses a lens component L₃ " having aconcave surface r₆ on the object side for observing an object located ata short distance and an aperture stop having a smaller diameter isadapted so that the objective optical system for endoscopes has a largerdepth of field and permits observing an object located at a distanceshorter than the object distance of the objective optical system shownin FIG. 15. The fourth embodiment of the objective optical system forendoscopes according to the present invention has the numerical datawhich are listed below:

Embodiment 4

for observing object at long distance

f=1.001, image height=0.4926, f_(B) =0.038,

2ω=59.652°, object distance=-71.8422

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.4237                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 1.1197                                                                d.sub.2 = 0.5614                                                            r.sub.3 = 1.5074                                                                d.sub.3 = 0.7415                                                                           n.sub.2 = 1.80518                                                                          ν.sub.2 = 25.43                                r.sub.4 = ∞                                                               d.sub.4 = 0.5297                                                            r.sub.5 = ∞ (stop)                                                        d.sub.5 = 0.0000                                                            r.sub.6 = ∞                                                               d.sub.6 = 0.5297                                                                           n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.7 = ∞                                                               d.sub.7 = 0.3390                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.4555                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = -2.6822                                                               d.sub.9 = 0.2119                                                            r.sub.10 = 2.2574                                                               d.sub.10 = 0.8475                                                                          n.sub.5 = 1.60311                                                                          ν.sub.5 = 60.70                                r.sub.11 = -1.1716                                                              d.sub.11 = 0.3178                                                                          n.sub.6 = 1.84666                                                                          ν.sub.6 = 23.78                                r.sub.12 = -1.9513                                                              d.sub.12 = 0.3814                                                           r.sub.13 = ∞                                                              d.sub.13 = 0.6356                                                                          n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0173816556            ______________________________________                                    

for observing object at short distance

f=0.999, image height=0.4936, f_(B) =0.049,

2ω=59.644°, object distance=-9.3406

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.4246                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 1.1221                                                                d.sub.2 = 0.5626                                                            r.sub.3 = 1.5106                                                                d.sub.3 = 0.7431                                                                           n.sub.2 = 1.80518                                                                          ν.sub.2 = 25.43                                r.sub.4 = ∞                                                               d.sub.4 = 0.5308                                                            r.sub.5 = ∞ (stop)                                                        d.sub.5 = 0.0000                                                            r.sub.6 = 15.2686                                                               d.sub.6 = 0.5308                                                                           n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.7 = ∞                                                               d.sub.7 = 0.3397                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.4565                                                                           n.sub.4 = 1.88300                                                                          ν.sub.4 = 40.78                                r.sub.9 = -2.6879                                                               d.sub.9 = 0.2123                                                            r.sub.10 = 2.2622                                                               d.sub.10 = 0.8493                                                                          n.sub.5 = 1.60311                                                                          ν.sub.5 = 60.70                                r.sub.11 = -1.1741                                                              d.sub.11 = 0.3185                                                                          n.sub.6 = 1.84666                                                                          ν.sub.6 = 23.78                                r.sub.12 = -1.9554                                                              d.sub.12 = 0.3822                                                           r.sub.13 = ∞                                                              d.sub.13 = 0.6369                                                                          n.sub.7 = 1.51633                                                                          ν.sub.7 = 64.15                                r.sub.14 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0224567287            |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0.0001341112                                                              ______________________________________                                    

In the fourth embodiment also, a surface r₆ to be used for observing theobject located at the long distance is planar, whereas a surface r₆ forobserving the object located at the short distance is convex.

FIG. 17 and FIG. 18 show sectional views illustrating compositions of anobjective optical system for. endoscopes which is preferred as the fifthembodiment of the present invention. The objective optical system forendoscopes is equipped with a side viewing type leading end adaptor forobserving an object located at a long distance in a condition shown inFIG. 17, whereas the objective optical system is equipped with a sideviewing type leading end adaptor for observing an object located at ashort distance in another condition shown in FIG. 18.

The objective lens system for endoscopes shown in FIG. 17 is a leadingend adaptor type objective lens system comprising a leading end adaptorwhich is composed of a negative lens component L₁, a side viewing prismP consisting of two prisms P₁ and P₂ cemented to each other, a positivelens component L₂, an aperture stop and a focal point adjusting lenscomponent L₃ ; and a cover glass plate C, a positive lens component L₄,a cemented lens component L₅ which consists of a positive lens elementL₅ ' and a negative lens element L₅ ", a cover glass plate C and animage guide fiber bundle IG for leading an image to an eyepiece lenscomponent which are disposed in the main body of an endoscope. In theobjective lens system shown in FIG. 18, a focal point adjusting lenscomponent L₃ ' which has a convex surface r₁₀ on the object side isadopted in place of the focal point adjusting lens component L₃ used inthe objective lens system shown in FIG. 17. Both the objective lenssystems have a common field angle of 120°.

FIG. 19 and FIG. 20 show sectional views illustrating compositions of anobjective optical system for endoscopes which is preferred as the sixthembodiment of the present invention. The objective lens system shown inFIG. 19 is equipped with a direct viewing type leading end adaptor forobserving an object located at a long distance, whereas the objectivelens system shown in FIG. 20 uses a direct viewing type leading endadaptor for observing an object located at a short distance. Theobjective lens system shown in FIG. 19 is a leading end adaptor typeobjective lens system comprising a leading end adaptor which consists,in order from the object side, of a negative lens component L₁, apositive lens component L₂, an aperture stop and a focal point adjustinglens component L₃ ; and a cover glass plate C, a positive lens componentL₄, a cemented lens component L₅ consisting of a positive lens elementL₅ ' and a negative lens element L₅ ", and a cover glass plate C whichare disposed in the main body of an endoscope; an image guide fiberbundle IG for leading an image to an eyepiece lens component. Further,in the objective lens system shown in FIG. 20, a focal point adjustinglens component L₃ ' which has an image side surface r₇ having curvaturelower than that on an image side surface of the focal point adjustinglens component L₃ shown in FIG. 19 so that the objective optical systemfor endoscopes is focused on an object located at a short distance.These objective lens systems have a field angle of 90°.

FIG. 21 and FIG. 22 show sectional views illustrating compositions ofthe seventh embodiment of the objective optical system for endoscopesaccording to the present invention. FIG. 21 shows the objective opticalsystem in a condition where it is equipped with a direct viewing typeadaptor for observing an object located at a long distance, whereas FIG.22 shows the objective optical system in another condition where it isequipped with a direct viewing type adaptor for observing an objectlocated at a short distance. The objective optical system shown in FIG.21 is a leading end adaptor type objective optical system for endoscopescomprising: a leading end adaptor which consists, in order from theobject side, of a positive lens component L₁, a cemented lens componentL₂ consisting of a positive lens element L₂ ' and a negative lenselement L₂ ", a focal point adjusting lens component L₃ and an aperturestop AS; a positive lens component L₄ ; a cemented lens component L₅which consists of a positive lens element L₅ ' and a negative lenselement L₅ "; a cover glass plate C; and an image guide fiber bundle IG.The objective optical system shown in FIG. 22 adopts a focal pointadjusting lens component L₃, having a convex surface r₂ on the imageside in place of the focal point adjusting lens component L₃ shown inFIG. 21 and an aperture stop which has a smaller diameter for increasinga depth of field. This objective optical system has a field angle of30°. In addition, the aperture stops are disposed in the seventhembodiment at a location which is different from those selected for thefirst through sixth embodiments described above.

The fifth through seventh embodiments of the present invention have thenumerical data which are listed below:

Embodiment 5

for observing object at long distance

f=1.000, image height=0.8688, f_(B) =0.046,

2ω=119.486°, object distance=-22.2094

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.5178                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 2.1197                                                                d.sub.2 = 0.6329                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.1726                                                            r.sub.4 = ∞                                                               d.sub.4 = 6.3291                                                                           n.sub.2 = 1.88300                                                                          ν.sub.2 = 40.78                                r.sub.5 = ∞                                                               d.sub.5 = 0.0575                                                            r.sub.6 = 5.4833                                                                d.sub.6 = 0.5754                                                                           n.sub.3 = 1.84666                                                                          ν.sub.3 = 23.78                                r.sub.7 = ∞                                                               d.sub.7 = 0.4258                                                            r.sub.8 = ∞ (stop)                                                        d.sub.8 = 0.0345                                                            r.sub.9 = ∞                                                               d.sub.9 = 0.4603                                                                           n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.10 = ∞                                                              d.sub.10 = 0.5984                                                           r.sub.11 = ∞                                                              d.sub.11 = 0.4603                                                                          n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                                r.sub.12 = ∞                                                              d.sub.12 = 0.2301                                                           r.sub.13 = ∞                                                              d.sub.13 = 0.8055                                                                          n.sub.6 = 1.51633                                                                          ν.sub.6 = 64.15                                r.sub.14 = -3.6318                                                              d.sub.14 = 0.2647                                                           r.sub.15 = 2.8573                                                               d.sub.15 = 1.9102                                                                          n.sub.7 = 1.77250                                                                          ν.sub.7 = 49.66                                r.sub.16 = -2.8573                                                              d.sub.16 = 0.4028                                                                          n.sub.8 = 1.78472                                                                          ν.sub.8 = 25.68                                r.sub.17 = 9.0909                                                               d.sub.17 = 0.7020                                                           r.sub.18 = ∞                                                              d.sub.18 = 0.7250                                                                          n.sub.9 = 1.51633                                                                          ν.sub.9 = 64.15                                r.sub.19 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0006350306            ______________________________________                                    

for observing object at short distance

f=1.000, image height=0.8830, f_(B) =0.026,

2ω120.688°, object distance=-7.6023

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.5263                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 2.1544                                                                d.sub.2 = 0.6433                                                            r.sub.3 = ∞                                                               d.sub.3 = 0.1754                                                            r.sub.4 = ∞                                                               d.sub.4 = 6.4327                                                                           n.sub.2 = 1.88300                                                                          ν.sub.2 = 40.78                                r.sub.5 = ∞                                                               d.sub.5 = 0.0585                                                            r.sub.6 = 5.5731                                                                d.sub.6 = 0.5848                                                                           n.sub.3 = 1.84666                                                                          ν.sub.3 = 23.78                                r.sub.7 = ∞                                                               d.sub.7 = 0.4327                                                            r.sub.8 = ∞ (stop)                                                        d.sub.8 = 0.0351                                                            r.sub.9 = ∞                                                               d.sub.9 = 0.5848                                                                           n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.10 = -46.7626                                                             d.sub.10 = 0.4912                                                           r.sub.11 = ∞                                                              d.sub.11 = 0.4678                                                                          n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                                r.sub.12 = ∞                                                              d.sub.12 = 0.2339                                                           r.sub.13 = ∞                                                              d.sub.13 = 0.8187                                                                          n.sub.6 = 1.51633                                                                          ν.sub.6 = 64.15                                r.sub.14 = -3.6912                                                              d.sub.14 = 0.2690                                                           r.sub.15 = 2.9041                                                               d.sub.15 = 1.9415                                                                          n.sub.7 = 1.77250                                                                          ν.sub.7 = 49.66                                r.sub.16 = -2.9041                                                              d.sub.16 = 0.4094                                                                          n.sub.8 = 1.78472                                                                          ν.sub.8 = 25.68                                r.sub.17 = 9.2398                                                               d.sub.17 = 0.7135                                                           r.sub.18 = ∞                                                              d.sub.18 = 0.7368                                                                          n.sub.9 = 1.51633                                                                          ν.sub.9 = 64.15                                r.sub.19 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0020988779            |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0.010059756                                                               ______________________________________                                    

Embodiment 6

for observing object at long distance

f=1.000, image height=0.7045, f_(B) =0.046,

2ω=90.806°, object distance=-30.5400

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.3724                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 2.1726                                                                d.sub.2 = 3.2464                                                            r.sub.3 = 2.2346                                                                d.sub.3 = 0.4655                                                                           n.sub.2 = 1.51633                                                                          ν.sub.2 = 64.15                                r.sub.4 = ∞                                                               d.sub.4 = 0.0186                                                            r.sub.5 = ∞ (stop)                                                        d.sub.5 = 0.4221                                                            r.sub.6 = ∞                                                               d.sub.6 = 0.3724                                                                           n.sub.3 = 1.88300                                                                          ν.sub.3 = 40.78                                r.sub.7 = 8.7232                                                                d.sub.7 = 0.5400                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.2483                                                                           n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.9 = ∞                                                               d.sub.9 = 0.1241                                                            r.sub.10 = ∞                                                              d.sub.10 = 0.6518                                                                          n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                                r.sub.11 = -2.6071                                                              d.sub.11 = 0.2173                                                           r.sub.12 = 2.1837                                                               d.sub.12 = 1.5518                                                                          n.sub.6 = 1.72916                                                                          ν.sub.6 = 54.68                                r.sub.13 = -1.9056                                                              d.sub.13 = 0.3228                                                                          n.sub.7 = 1.84666                                                                          ν.sub.7 = 23.78                                r.sub.14 = 25.4836                                                              d.sub.14 = 0.5338                                                           r.sub.15 = ∞                                                              d.sub.15 = 0.7697                                                                          n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0358112952            ______________________________________                                    

for observing object at short distance

f=1.000, image height=0.7184, f_(B) =0.016,

2ω=92.434°, object distance=-8.3464

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.3797                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = 2.2152                                                                d.sub.2 = 3.3102                                                            r.sub.3 = 2.2785                                                                d.sub.3 = 0.4747                                                                           n.sub.2 = 1.51633                                                                          ν.sub.2 = 64.15                                r.sub.4 = ∞                                                               d.sub.4 = 0.0190                                                            r.sub.5 = ∞ (stop)                                                        d.sub.5 = 0.4304                                                            r.sub.6 = ∞                                                               d.sub.6 = 0.3797                                                                           n.sub.3 = 1.88300                                                                          ν.sub.3 = 40.78                                r.sub.7 = 11.1652                                                               d.sub.7 = 0.5506                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.2532                                                                           n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.9 = ∞                                                               d.sub.9 = 0.1266                                                            r.sub.10 = ∞                                                              d.sub.10 = 0.6646                                                                          n.sub.5 = 1.51633                                                                          ν.sub.5 = 64.15                                r.sub.11 = -2.6582                                                              d.sub.11 = 0.2215                                                           r.sub.12 = 2.2266                                                               d.sub.12 = 1.5823                                                                          n.sub.6 = 1.72916                                                                          ν.sub.6 = 54.68                                r.sub.13 = -1.9430                                                              d.sub.13 = 0.3291                                                                          n.sub.7 = 1.84666                                                                          ν.sub.7 = 23.78                                r.sub.14 = 25.9835                                                              d.sub.14 = 0.5443                                                           r.sub.15 = ∞                                                              d.sub.15 = 0.7848                                                                          n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.16 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0305184478            |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0.0179283307                                                              ______________________________________                                    

Embodiment 7

for observing object at long distance

f=1.000, image height=0.2657, f_(B) =0.010,

2ω=30.10°, object distance=-28.9013

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.2000                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = -4.9310                                                               d.sub.2 = 0.1143                                                            r.sub.3 = 1.6052                                                                d.sub.3 = 0.2685                                                                           n.sub.2 = 1.72000                                                                          ν.sub.2 = 43.70                                r.sub.4 = -3.5196                                                               d.sub.4 = 0.1214                                                                           n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.5 = 1.1709                                                                d.sub.5 = 0.1429                                                            r.sub.6 = -1.4803                                                               d.sub.6 = 0.2857                                                                           n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.7 = ∞                                                               d.sub.7 = 0.0171                                                            r.sub.8 = ∞ (stop)                                                        d.sub.8 = 0.1829                                                            r.sub.9 = ∞                                                               d.sub.9 = 0.2457                                                                           n.sub.5 = 1.88300                                                                          ν.sub.5 = 40.78                                r.sub.10 = -1.4469                                                              d.sub.10 = 0.1143                                                           r.sub.11 = 1.2177                                                               d.sub.11 = 0.4571                                                                          n.sub.6 = 1.60311                                                                          ν.sub.6 = 60.70                                r.sub.12 = -0.6320                                                              d.sub.12 = 0.1714                                                                          n.sub.7 = 1.84666                                                                          ν.sub.7 = 23.78                                r.sub.13 = -1.0526                                                              d.sub.13 = 0.2057                                                           r.sub.14 = ∞                                                              d.sub.14 = 0.3429                                                                          n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.15 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.0145309178            ______________________________________                                    

for observing object at short distance

f=1.000, image height=0.2722, f_(B) =0.010,

2ω=30.10°, object distance=-9.3677

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.2049                                                                           n.sub.1 = 1.88300                                                                          ν.sub.1 = 40.78                                r.sub.2 = -5.8920                                                               d.sub.2 = 0.1171                                                            r.sub.3 = 1.6246                                                                d.sub.3 = 0.2804                                                                           n.sub.2 = 1.72000                                                                          ν.sub.2 = 43.70                                r.sub.4 = -2.4772                                                               d.sub.4 = 0.1244                                                                           n.sub.3 = 1.51633                                                                          ν.sub.3 = 64.15                                r.sub.5 = 1.1555                                                                d.sub.5 = 0.1464                                                            r.sub.6 = -1.7339                                                               d.sub.6 = 0.2927                                                                           n.sub.4 = 1.51633                                                                          ν.sub.4 = 64.15                                r.sub.7 = -6.7785                                                               d.sub.7 = 0.0176                                                            r.sub.8 = ∞ (stop)                                                        d.sub.8 = 0.1874                                                            r.sub.9 = ∞                                                               d.sub.9 = 0.2518                                                                           n.sub.5 = 1.88300                                                                          ν.sub.5 = 40.78                                r.sub.10 = -1.4824                                                              d.sub.10 = 0.1171                                                           r.sub.11 = 1.2477                                                               d.sub.11 = 0.4684                                                                          n.sub.6 = 1.60311                                                                          ν.sub.6 = 60.70                                r.sub.12 = -0.6475                                                              d.sub.12 = 0.1756                                                                          n.sub.7 = 1.84666                                                                          ν.sub.7 = 23.78                                r.sub.13 = -1.0785                                                              d.sub.13 = 0.2108                                                           r.sub.14 = ∞                                                              d.sub.14 = 0.3513                                                                          n.sub.8 = 1.51633                                                                          ν.sub.8 = 64.15                                r.sub.15 = ∞                                                            |Δf.sub.B6 /f.sub.6.sup.2 | = 0.013853912             |{sin.sup.-1 (h/f) - sin.sup.-1 (h/f')}/sin.sup.-1 (h/f).vertline    . = 0                                                                         ______________________________________                                    

In the first through seventh embodiments of the present invention whichhave been described above, the objective lens systems for observing theobjects located at the long distances are fundamentally the same as theobjective lens systems for observing the objects located at the shortdistances, except for the focal point adjusting lens components L₃ andL₃ ' which are different from one another. However, the numerical dataof these objective lens systems other than those of the focal pointadjusting lens components are different from one another when thenumerical data are normalized to focal lengths of the objective lenssystems as wholes since the objective lens systems for observing theobjects located at the long distances have focal lengths which areslightly different from those of the objective lens systems forobserving the objects located at the short distances. As a result, thenumerical data of the objective optical systems for endoscopes, exceptfor those of the focal point adjusting lens components, are differentfrom one another though the numerical data are actually the same as oneanother.

Though the leading end adaptor type objective optical systems forendoscopes have been preferred as the first through seventh embodimentsdescribed above, the present invention is applicable also to the adaptortype objective optical systems for endoscopes. Speaking concretely, itis possible to exchange only the focal point adjusting lens componentand the aperture stop with others though the focal point adjusting lenscomponent and the lens system disposed before the aperture stop areconfigured as an integral unit which is attachable and detachable to andfrom the main body of an endoscope in each of the embodiments describedabove.

In particular cases where endoscopes are to be used for observinglocations under influences due to radiations, for example, interiors ofnuclear reactors, it is necessary to take the following points intoconsideration. When energy of a radiation such as X-ray or gamma-raydrives out electrons from any kinds of ions composing glass materials,the electrons are accommodated into lattice defects in a glass structurewhich have positive electric charges suited for capturing the electrons,mainly cavities of oxygen ions, thereby producing characteristicabsorption corresponding to the F center which appears in crystals ofrock salt or the like. In cases of glass materials, locations forcoupling with oxygen ions are of several types dependently on specificproperties of internal structures of the glass materials and absorptiondue to continuous deviation caused by irregularities of atomicarrangement is overlapped with the characteristic absorption, whereby itis general that clear independent absorption is scarecely produced, butcontinuous absorption curves are formed. As a result, the glassmaterials are colored in brown, pink, etc., and exhibit remarkablylowered transmittance, thereby making it impossible to observe objectsthrough the objective optical systems for endoscopes.

As glass materials which have radiation-resistant characteristics orwhich are not colored by radiations, there are known those which areprepared by adding cerium oxide to glass materials containing lead orbarium at high ratios. However, the glass materials containing ceriumare yellowish before irradiation with radiations due to absorption ofrays having short wavelengths within the visible region under presenceof Ce⁴⁺. Heavy flint glass materials which have high refractive indicesexhibit this tendency more remarkably and are strongly yellowish.Accordingly, images are strongly yellowish and favorable observations ofthese images are impossible when the objective optical systems forendoscopes are made of glass materials which contain cerium oxide athigh ratios or have high refractive indices or when the optical systemshave long optical paths.

FIG. 39 through FIG. 44 illustrate spectroscopic transmittance ofradiation-resistant glass materials (10 mm thick) containing ceriumoxide which are mentioned as items (1) through (6) below:

(1) Cerium oxide added to BK7 nd: 1.51630 νd: 64.36

(2) Cerium oxide added to SK nd: 1.61222 νd: 58.14

(3) Cerium oxide added to F2 nd: 1.62004 νd: 36.38

(4) Cerium oxide added to LAK9 nd: 1.69089 νd: 54.83

(5) Cerium oxide added to SF1 nd: 1.71414 νd: 29.72

(6) Cerium oxide added to Fn3 nd: 1.84738 νd: 23.86

As is seen from FIG. 39 to FIG. 44, glass materials which have higherrefractive indics exhibit lower transmittance at the short wavelengthsand are yellowish more remarkably. When objective optical systems forendoscopes are to be used for observing objects under influences due toradiations, it is necessary to manufacture objective lens systems byselecting radiation-resistant glass materials which has high refractiveindices and configuring lens components so as to be thin for preventingimages observed through the objective lens systems from beingdiscolored.

The radiation-resistant glass materials containing cerium oxide whichare listed as items (1) through (6) above exhibit transmittance listedbelow at 450 nm and 500 nm:

(Before irradiation with a radiation)

    ______________________________________                                                    450 nm                                                                              500 nm                                                      ______________________________________                                        (1)           90%     91%                                                     (2)           84%     88%                                                     (3)           85%     89%                                                     (4)           78%     85%                                                     (5)           52%     81%                                                     (6)            2%     52%                                                     ______________________________________                                    

(A: Immediately after irradiation with a radiation B: Five days afterirradiation with a radiation)

    ______________________________________                                        450 nm                     500 nm                                             ______________________________________                                        (1)     A     75%       B   77%    A 84% B 85%                                (2)     A     60%       B   65%    A 75% B 80%                                (3)     A     69%       B   73%    A 82% B 85%                                (4)     A     32%       B   36%    A 68% B 73%                                (5)     A     15%       B   21%    A 64% B 70%                                (6)     A      0%       B    0%    A 27% B 33%                                ______________________________________                                    

As is understood from the tables shown above, these radiation-resistantglass materials do not allow remarkable lowering of transmittancethereof though allows slight lowering of transmittance at the shorterwavelength after irradiation with a radiation. Further, thetransmittance of these glass materials is a little improve with lapse oftime as is seen from the table listing transmittance values five daysafter the irradiation with the radiation.

An embodiment of the objective optical system for endoscopes accordingto the present invention which is configured so as to take the pointdescribed above into consideration will be described below:

Embodiment 8

f=1.019, F/4.245, image height=0.4984,

f_(B) =0.057, object distance=-9.4307

    ______________________________________                                        r.sub.1 = ∞                                                               d.sub.1 = 0.4205                                                                           n.sub.1 = 1.84738                                                                          ν.sub.1 = 23.86                                r.sub.2 = 0.9715                                                                d.sub.2 = 0.5698                                                            r.sub.3 = 1.4310                                                                d.sub.3 = 0.8199                                                                           n.sub.2 = 1.84738                                                                          ν.sub.2 = 23.86                                r.sub.4 = ∞                                                               d.sub.4 = 0.5359                                                            r.sub.5 = ∞ (stop)                                                        d.sub.5 = 0.0000                                                            r.sub.6 = 6.1696                                                                d.sub.6 = 0.5205                                                                           n.sub.3 = 1.51630                                                                          ν.sub.3 = 64.46                                r.sub.7 = ∞                                                               d.sub.7 = 0.3108                                                            r.sub.8 = ∞                                                               d.sub.8 = 0.4707                                                                           n.sub.4 = 1.84738                                                                          ν.sub.4 = 23.86                                r.sub.9 = -4.7539                                                               d.sub.9 = 0.1973                                                            r.sub.10 = 1.7755                                                               d.sub.10 = 0.8298                                                                          n.sub.5 = 1.61222                                                                          ν.sub.5 = 58.14                                r.sub.11 = -0.8794                                                              d.sub.11 = 0.3176                                                                          n.sub.6 = 1.84738                                                                          ν.sub.6 = 23.86                                r.sub.12 = -1.6511                                                              d.sub.12 = 0.3899                                                           r.sub.13 = ∞                                                              d.sub.13 = 0.6431                                                                          n.sub.7 = 1.51630                                                                          ν.sub.7 = 64.46                                r.sub.14 = ∞                                                            ______________________________________                                    

The eighth embodiment of the objective optical system for endoscopesaccording to the present invention is a direct viewing type objectiveoptical system which has the composition shown in FIG. 37 and isconfigured for observing an object located at a long distance. Theeighth embodiment permits observing an object located at a shortdistance when an aperture stop and a lens component disposed immediatelyafter this aperture stop are exchanged with others.

In each of the first through eighth embodiments of the present inventiondescribed above, the focal point adjusting lens component may be omittedwhen a plane parallel plate is adopted as this lens component.

The objective optical system for endoscopes according to the presentinvention permits adjusting a distance to an object to be observedsimply by exchanging a lens component disposed in the vicinity of anaperture stop with another lens component. Further, the objectiveoptical system for endoscopes according to the present invention permitsselecting an optimum depth of field simply by changing a diameter of theaperture stop along with the exchange of the lens component.

We claim:
 1. An endoscope comprising:an endoscope body; a master lensunit which is fixed to a distal end of said endoscope body for formingan image of an object; and a plurality of adaptor units each of whichcomprises lens components disposed on one optical axis and an aperturestop such that said adaptor units have focal lengths different from oneanother; wherein said adaptor units are attachable and detachable to andfrom said distal end of said endoscope body, wherein a first objectiveoptical system defined by lens components from a first adapter unit fromsaid plurality of adaptor units and said master lens unit if said firstadaptor unit is attached to an object side of said master lens unit,wherein a focal length of said first objective optical system equippedwith said first adaptor unit is different from a focal length of asecond objective optical system equipped with a second adaptor unit, andwherein the lens component which is disposed in the vicinity of saidaperture stop of said first adaptor unit may selectively vary from thelens component which is disposed in the vicinity of said second adaptorunit.
 2. An endoscope according to claim 1, wherein said aperture stopis disposed on the object side and proximate to a first lens componentof said first adaptor unit, wherein the first lens component is thecomponent closest to said master lens unit; andwherein the focal lengthof said first adaptor lens component is selectively varied from a secondlens component which is the closet second adaptor lens component to saidmaster lens unit.
 3. An endoscope according to claim 2, wherein anobjective optical lens system comprised of said master lens unit andsaid adaptor unit attached to said master lens unit is defined as afirst objective optical lens system and the other objective optical lenssystem consisting of said master lens unit and said second adaptor unitattached to said master lens unit is defined as a second objectiveoptical lens system, said first objective optical system and said secondobjective optical system have substantially the same field angle butdifferent observation distance.
 4. An endoscope according to claim 2,wherein aperture diameters of said aperture stops of said plurality ofadaptor units are different in accordance with said focal length of saidrearmost lens component.
 5. An endoscope according to claim 2, whereinsaid plurality of adaptor units includes adaptor units whose angle offields are different from one another and adaptor units whose viewingdirections are different from one another.
 6. An endoscope according toclaim 2, wherein said master lens unit has no focusing function and eachof said lens components is always fixed on said optical axis.